Renewable sources of hydrocarbons are becoming of increasing importance. In particular naphthenic hydrocarbons, which represent only some 5% of known crude oil reserves, are currently in declining supply with the known available supplies becoming more difficult to recover and refine. One primary application of refined naphthenic oils is in the production of electrical insulating oil, commonly referred to as transformer oils. This oil acts as a primary insulator in the transformers and associated equipment that form the critical transport and delivery infrastructure for the worlds electricity supply. The current annual consumption rate for electrical insulating oils is estimated to be 1.35 billion liters and growing. Disposal of used electrical insulating oil is occurring at a rate likely in excess of around 1 billion liters per annum and the stock of oil in service awaiting final disposal is in the range of 20 billion liters. Capturing and re-processing this material reduces the amount of materials that needs to be disposed of and also reduces the need to extract and refine further replacement crude oil.
Used electrical insulating or transformer oils are predominantly disposed of for secondary uses including incineration as a supplementary fuel or combustion directly in energy recovery. Smaller volumes of higher quality segregated used transformer oils are in some cases filtered and dried for re-use as cheaper second quality oils. Such disposal methods are failing to meet the increasing demand for more efficient and high quality recycling and materials recovery. Since 2005 one company, Hydrodec Group, has been refining used and PCB contaminated transformer oils then subsequently further processing the refined product to produce new electrical insulating oil.
The drive for increased efficiency in electrical equipment is demanding the production of more consistent electrical insulating oils resistant to oxidation, having strong electrical properties and good compatibility with other materials of construction. These properties are created mainly through hydroprocessing to deliver higher levels of saturates and more controlled sulphur levels without compromising the viscosity and solvency of the oil. These same properties are also consistent with other applications for naphthenic base oils including for example in agriculture. Technology for re-processing used transformer oils also needs to progress with the changing mix of used transformer oils including ester oils and other contaminants.
Used electrical insulating oils degrade during use through oxidation, and other complex reactions in the presence of metals and other equipment components and also through exposure to electrical arcing and other strong electrical field effects. They may also contain additives from the original new oil including oxidation inhibitors, metal passivators and polychlorinated biphenyls. Catalytic hydroprocessing of the used insulating oils under the appropriate conditions reduces the oxidised oils and removes additives remaining in the oil. It also, in the presence of a basic nitrogen containing compound, dehalogenates the oils while the basic nitrogen containing compound neutralises the acid sites formed during hydroprocessing thereby protecting the catalyst and catalyst support from acid attack and protecting the oil from hydrocracking side reactions.
An earlier process for refining used transformer oils is described in PCT/AU93/00682. This process included a method for removing a halide from a halide containing compound and oxygen from an oxidised organic compound in an organic solvent, permitting recovery of the organic compound and the organic solvent in a halide and oxygen free condition. The practical expression of this process resulted in a system for processing and refining used electrical insulating oil to remove the halogen from PCB and oxygen from aged oil to produce a refined dehalogenated oil product.
The process of PCT/AU93/00682 does not produce a product suitable for use as new insulating oil since the product contained reduced and reactive volatile and semi-volatile sulphur compounds and other oil species. The oil requires further processing to correct these properties before it achieves a quality that meets agreed technical standards defining new naphthenic base oils suited for use in new electrical insulating oil and similar applications. Further processing of the product from this process is required to address quality deficiencies in the product relating to oxidative stability and corrosivity.
There is therefore a need for an improved process in order to at least partially overcome the above deficiencies.